Damp rod construction for cathode ray tube grid structure



June 18, 1957 PATTERSON 2,796,546

DAMP ROD CONSTRUCTION FOR CATHODE RAY TUBE GRID STRUCTURE Filed June 29,1953 2 Sheets-Sheet 1 INVENTOR. Howard A. Fame/"$00 June 18, 1957 H, R,PATTERSON 2,796,546

DAMP ROD CONSTRUCTION FOR CATHODE RAY TUBE GRID STRUCTURE Filed June 29,1953 2 Sheets-Sheet 2 INVEN TOR. Howard E Puffs/"son United StatesPatent? O DAIVIP ROD CONSTRUCTION FOR CATHODE RAY TUBE GRID STRUCTUREHoward R. Patterson, Oakland, Calif., assignor to Chromatic TelevisionLaboratories, Inc., New York, N. Y., a corporation of CaliforniaApplication June 29, 1953, Serial No. 364,778

7 Claims. (Cl. 313-78) The present invention relates to cathode-raytubes of the type adapted to eifect the reconstitution of polychromeimages. More particularly, the invention relates to cathode-ray tubeshaving a grid of coplanar parallel wires positioned adjacent to astriped phosphor screen or target electrode. It also relates to meansfor enhancing the color fidelity of the image reproduced on this screenby inhibiting any tendency the wires of the grid may have to vibrate asa result of the cyclic application of electrical potentials theretoand/or as a result of any shock excitation of either a physical orelectrical nature.

Cathode-ray tubes constructed with a grid of parallel wires locatedadjacent to a striped phosphor screen are already'known in the art andserve to focus the beam electrons into a pattern of thin parallel linesregistered with the phosphor strips of the screen. The PDF(postdeflection-focusing) type of cathode-ray tube operation has beenset forth by Ernest 0. Lawrence in various of his copending UnitedStates patent applications, such as Serial No. 219,213, filed April 4,1951, and Serial No. 234,190, filed June 29, 1951 (now respectively U.S. Patent No. 2,692,532, granted October 26, 1954, and U. S. Patent No.2,711,493, granted June 21, 1955).

In order to facilitate an understanding of the principles of the presentinvention, a brief description of one such form of single-gun PDF tubewill now be given. This description should be construed as exemplaryrather than limiting, since it will be seen that the invention isobviously applicable to tubes constructed along different lines. Ingeneral, however, the tube may incorporate a screen or target electrodemade up of a relatively large number of very narrow component-colorphosphor strips and laid down in a predetermined sequence and intendedto luminesce, when impacted by the cathode-ray beam, in colors such asred, green, blue, green, red, green, for example. Obviously, whenreference is hereinafter made to the color of a phosphor, what is meantis the color of the light emitted therefrom which reaches the eye of theobserver. The phosphors are then aluminized, or the screen in some othermanner is provided with an electrically conductive coating.

A grid assembly is located adjacent to such phosphor screen. The gridmay be made up of parallel coplanar wires, and so related to thephosphor strips that, in an electron-optical sense, there is a wirealigned with each blue strip, and similarly a wire aligned with each redstrip. The red wires are connected to a common terminal, while the bluewires are similarly joined together electrically.

Between the plane of the wire grid assembly and the conductive coatingon the phosphor screen, there may be established a relative differenceof potential of such magnitude and polarity as to create a series ofconverging cylindrical lenses for the electrons in the scanning beam.Such converging fields cause the beam electrons to form a fine linestructure on thephosphor screen, this line structure having no necessarydirect geometrical relationice It will now be appreciated that, as thebeam electrons travel from the electron gun they may be focussed by theabove-described lens structure into a series of lines parallel to thephosphor strips. If there is a zero potential difference between the redand blue terminals of the wire grid, then these lines formed by the beamelectrons may be caused to lie within the boundaries of the greenstrips. If the wires associated With the red strips are made positiverelative to the wires electron-optically related to the blue-strips, thebeam electrons will be de= flected, and the thin lines will now liewithin the boundaries of the red strips. Similarly, the electrons Willstrike the blue strips when the wires associated with such strips arerelatively positive with respect to the red wires. Different componentcoolrs are thus displayed 3C1 cording to the potential difference (ifany) existing between the two sections of the grid wire assembly.

Accordingly, color control in a cathode-ray tube having a grid assemblyof the above nature (whether used for PDF or not), is brought about by acyclic change in the potentials applied to selected wires of the grid,with the electrostatic charges on the wires exerting forces themagnitude of which varies as a function of this potential change. If'theforces thus exerted vary at a fre quency close to the natural resonantfrequency of the wires, the latter will vibrate, resulting in anoscillation of the line pattern on the phosphor screen. If the magnitudeof this oscillation is sufficiently great, color contamination and/ orelectrical shorting can occur. Even with relatively little wirevibration the electron beam may be defocussed, and image reproductionseriously impaired. It is of course, obvious that wire vibration mayalso result from electrical shocks received by the grid assembly, or asa result of physical shocks to which the entire cathode-ray tube may besubjected.

The above problem has been recognized. One solution is proposed in acopending United States patent application of James T. Vale, Serial No.252,664, filed October 23, 1951 (now U. S. Patent No. 2,721,288, grantedOctober 18, 1955), and assigned to the same assignee as the presentapplication. In the Vale disclosure, the vibration of such a wire gridis damped, and one preferred arrangement for carrying out this objectiveincludes an insulating cord or strand (which may be a ceramic thread)wound, or passed in-and-out, between the parallel conductors in a regionnear the wire frame or support.

The above-mentioned Vale method of reducing the amplitude of grid wirevibration by bringing into contact with the wires a mechanically lossymaterial is effective for many purposes Where some residual vibrationcan be tolerated. However, friction between the wires and the dampingmember necessitates the use of materials able in a United States patentapplication entitled Grid for- Color Television Tubes (also identifiedas Serial No. 343,887, filed March 23, 1953). This embodies theprinciple that the frequency of vibration of a supported wire is afunction of the distance between its supports. Hence, if a wire of givenlength (having a certain natural resonant frequency) is rigidly held atone or more points between its ends, then the wire segments between theconstraining points will have higher resonant frequencies correspondingto their shorter lengths. If these increased resonant frequencies aresufliciently higher than the driving frequency (i. e., the rate ofchange of potentials applied to the wires) then the tendency of the wireseg-- ments to vibrate will be materially reduced, and the amplitude ofany vibration which does occur will be much lower.

One structure designed in accordance with the teaching of the identifiedCook application comprises a node bar of insulating material, such asglass, extending across the grid wires, the latter being rigidly securedto the bar at spaced points.therealong. To eliminate the. electronshadow which would otherwise result from the presence of a solid objectin'the path of the scanning beam, the bar is given a conductive coatingover. the portion of its surface which is. out of contact withthe wires.The undesirable shadow region is thus filled in with electrons whichwould normally impinge other points on the target area. 7 7

Both the Vale and Cook arrangements operate satisfactorily in many tubetypes. However, with' advancesin tube designs and the trend toward.extremely large? 1 surface must be given a conductive= coating, andthen. this coating-. must' be connected to: a. point" of properpotential. v

It becomes possible, to dispensewith a: number: of the operations madenecessary by the employment of anode bar such as described above,through utilization of a plurality of straight rods, of some rigid.insulating material such as glass, which are interwoven between the gridwires in such a manner. thatthe latter are displacedvertically (normaltothe plane of: the target electrode) atevery rod, with a'djacentjwiresbeing offset in opposite directions; Such an? arrangement is describedin a copending United States patent application of Ernest 0. Lawrence,Serial No. 342,941, filed March '17, 1953, and also assigned to the sameassigneeas the present application.

It is additionally found, by establishing" a certain po tentialdifference between the electron gun 'of the cathoderay tube and the wiregrid, andalso by employing a selected composition for the rods, that anumber of the scanning beam electrons'are brought into that region ofthe target electrode which would otherwise be shadowed. Thus anarrangement ofthe type'described in the last-mentioned Lawrenceapplication not' only materially reduces vibration of the grid wires,but also substantially eliminates the shadow etfect without requiringnotched bars; cement, electrical coatings, or con ductors-for creatingand maintaining a predeterminedpo tential on the surface of thevibration-reducing components.

However, the linear configuration of the damp rods causes theinterweavingprocess to produce two substantially coplanar sets (orgroups) ofgrid wires, with alternate'wires being displaced in the samegeneral direction normal to the plane of the base plate. Application ofcolor switching voltagesto these two sets of wires may, in some cases,result inslight color fringing due to the difference in raster size ofthe individual component-color fields. This is dueto the .greater efiecton the electrons in the'scanning beam of the grid Wires lying nearest tothe electron gun 'ofthe cathode-ray tube, considered wtih respect to'thefurthest,.or hidde'nj" grid. These means may generally be said toinvolve use of voltages on the two sets ofgridwires which are unbalancedto that particular degree. required to bring the respective raster areasinto substantial coincidence.

It is, in many instances, desirable to incorporate within thecathode-ray tube means .for overcoming the adverse effects of grid wirevibration without at'the same time rigidly anchoring-each gridwire tothe damping'member, as suggested by Cook, or utilizing elementswhich-sep- 4' arate the grid wires into distinct planes, as proposed byLawrence. Such an expedient not only permits the cementitious bindingmaterial of the former arrangement to be dispensed with, along with thepossibility of lateral displacement of the parallel conductors, but alsoeliminates the unbalanced voltagesfor the two sets of grid wiresfrequently required by a structure designed in ac: cordance withLawrences teaching.

One solution of the problem set forth above is described in the presentapplication. It recognizes the desirability of maintaining a coplanarrelationship of the grid wires, and takes this into account. byemploying. at least one damping element the configuration of which isspecifically chosen so as not to disturb this grid wire relationship. Atthe same time, not only is Wire vibration reduced in magnitude, but, byextending the interweaving concept of Lawrence to a degree notattainable in the disclosure referred to,-the actual effectiveness ofthe damping action is greatly enhanced.

Oneobject of the present invention, therefore, is to: provide animproved'form of cathode-raytube suitable for the reconsitutiontofpolychrome images;

A further object of the inventioniis to substantially 7 completelyovercome, in a polychrome: cathode-ray. tube: having a grid structureof. coplanar parallel wires, anytendencytoward'vibration the wires of.the grid structure may possess either when color-changing potentials arecyclically applied thereto: or when. the grid structu'reis subjected toshocks of a physicaland/orelectrical nature;

An additional object of the:present invention istoaccomplish the aboveobjective while at the sametimemaintaining the coplanar relationship ofthe grid wires;

A still further object of: the present invention isto provide, in apolychrome. cathode-ray tube having a color-controlgrid. structure ofcoplanar parallel wires, at least one dampingi element of non-linearconfiguration interwoven with the Wires of-the' color-control grid.

.Fig. I is apartly schematic representation'of-one form:

of cathode-ray tube in which the present-invention may be incorporated;

Figure 2is an enlarged'view of a portion of Figure 1;

Figure 3 is aperspective view of a portionof the wire grid assembly ofFigure 1, showing in greater detail the interwoven relationshipbetweenthe" grid wires and damp rods;

Figure 4=is a sectional view of a portion of Figure 3 along the line4-4; and

vFigure 5 is a'plan- View ofap'ortion of Figure 3,showing'one-preferredassociationof the grid WlI'BS' andphosphor' strips.

Referringnow to Figure l of the drawings, there is generally indicatedbythe reference numeral'ltlj one type of cathode-ray tube-in'which thepresent invention may be incorporated. Thistub'e 10inolud'es-the usualcomponents for developing abeam of electrons; and for deflecting thiselectron-beam- 12 in substantially mutually perpendicular directions wasto trace a-rasteron the tube target electrode.

The target electrode-of't-ube 1-0, for ease of illustration, isdisclosed as formingpartfofa separateunit or assembly 14mounted in. anysuitable manner adjacent to the transparent end wall16 of the tube. endwall 16 when' suitably configured, may itself cornprise thetargefel'ect'rode if convenient or desirable. For certainconstructionaldetai'ls ofthe assembly 14, -reference is made toabove-mentioned Vale application, .Serial No. 252,664,. as -well as tofurther copending applications of Renn Zaphiropoulos, Serial 'No.307,435, filed September 2, 1952 (now U. S; Patent No. 2,683,833,gran-ted July 13,' 1954),. andSerial'No. 307,436, filed September 2,1952'. However, inasmuch .as:.these.constructional detailsformnopart'ofthe present invention, they willibe'omittedi from thedescription which" follows, audit will merelybe stated that the.assembly '14" whiohincludes.a'transparentr Obviously, however; the

base plate 18, a phosphor coating 20 thereon, and agrid of parallelcolor-control conductors 22 adjacent to the phosphor coating 20) ispositionedand supported within the tube so that the light produced byimpingement of the scanning beam 12 on the phosphor coating may beviewed by an observer through the transparent end wall 16 of thecathode-ray tube.

The base plate 18 may be of glass or other suitable material. Thephosphor coating 20 is preferably in the form of a plurality of narrowstrips which have the property of fiuorescing in different componentcolors of the image to be reconstituted, these colors, for example,being red, green and blue. These strips are laid down side-byside in apredetermined chromatic sequence. As best shown in Figures 3 and 4, theorder chosen for illustration is red, green, blue, green, red, green,etc. This order, however, forms no specific part of the presentinvention, but is suggested as one order which has proved to besatisfactory. The phosphor coating 20 is then aluminized or otherwiseprovided with a thin film of electrically-conductive material on thesurface toward the source of the impinging electrons.

The color-control grid adjacent to the target surface 20 is composed ofa plurality of linear conductors, such as the parallel wires 22, alignedwith the phosphor strips in a manner best shown in Figures 3 and 5.(Only a small section of the striped phosphor surface 29 of the targetelectrode is illustrated in Figure 3 in order to permit a. clear showingof the grid wire relationships.) That is, there is a grid wireassociated with each red and blue phosphor strip, but none with thegreen. By cyclically varying the voltage of the red wires with respectto the voltage of the blue wires, different chromatic aspects of animage are successively presented. In this connection, it must be kept inmind that the drawings of the present application are not to scale, andthe relative dimensions and spacings of the illustrated components areintentionally distorted for ease of presentation. In general, though,each pair of wires may, in an electronoptical sense, he considered assubtending strip areas constituting one color cycle.

In a preferred form of tube design, a potential is applied to theconductive coating on the phosphor surface 20 which is relativelypositive with respect to the average, or D.-C., potential of the wires22 of the grid assembly. This gives rise to a plurality of cylindricalelectrostatic lenses, which serve to focus the electrons of the scanningbeam 12 in a series of fine lines registered with the phosphor strips.However, the present invention is obviously applicable to cases wherethe wires 22 serve either as a color-changing device alone, as willsubsequently appear, or as an electrostatic lens assembly per se, asshown for example in patent application, Serial No. 234,190 abovereferred to.

Although any suitable method may be employed for positioning the wires22 so that they are adjacent to the phosphor-coated surface 20 of thetarget electrode, a pair of bars 24 and 26 is shown, each of these barshaving on its upper surface a series of equally-spaced grooves foraligning the wires 22 and preventing internal movement at such points.The wires are respectively held taut (as best shown in Figures 1 and 2)by a plurality of hooks forming part of two retaining assemblies '28secured to the under surface of the transparent base plate 18 beyond theboundaries of the image raster area. This general type of constructionis described and claimed in Zaphiropoulos application Serial No.307,435, referred to above.

It has been indicated that one of the principal features of the presentinvention consists in substantially completely overcoming any tendencytoward vibration the wires of a color-control grid assembly of the classdescribed may possess by interweaving one or more rigid rod-"likemembers between the wires of the color-control assembly, while at thesame time retaining the coplanar wire rela- 6 tionship. One sucharrangement is shown in Figures l through 5.

In this construction, three insula g rods 30, 32 and 34 of circularcross-sect-ion have been chosen for illustration, although the rod 32alone will produce results as set forth below. In each case, however,the rods extend substantially transversely to the grid wires 22 and areinterwoven therebetween; that is-over one wire, under the next, over thefollowing wire, etc. Figure 3, 4 and 5 bring out this intervowenrelationship most clearly.

:In order to maintain a coplanar relationship of the grid wires 22, aparticular configuration is imparted to each of the damp rods 30, 32 and34. As perhaps best shown in Figure 4, this configuration may be termedzig zag in nature for convenience of description. Expressed differently,a rod which would otherwise be essentially linear is bent at pointscorresponding in number to the number of grid wires with which the rodis to be interwoven. The direction of bending is the same at alternatepoints; that is in, out, in, out, etc. as again perhaps best shown inFigure 4. The-result is a rod of undulating form, and, if the amount bywhich the rod is bent is chosen so that L1=the distance from the innersurface of the damp rod at any selected convolution k to thelongitudinal axis xx of the damp rod L2=the distance from the innersurface of the damp rod at convolutions adjoining convolution k to thelongitudinal axis x-x of the damp rod D=the diameter of the damp rodthen there will be good surface contact between the rod and each of thegrid wires 22 with which it is interwoven.

Each of the damp rods 30, 32 and 34 is not only interwoven with the gridwires 22 but in addition is ofiset with respect to each adjoining damprod or rods in the sense that corresponding convolutions of adjoiningrods extend in opposite directions. The construction accordingly is onein which the rod 32, for example, overlies those particular grid wireswhich the rods 30 and 34 go under. Reference to Figure 5 illustratesthis point, and, in Figure 4, the side view of rods 30 and 32 brings outthat the former (which lies in back of the rod 32) contacts each gridwire at a point which is diametrically opposed to the point at whicheach grid wire is contacted by the rod 32. The rod 34, although notshown in Figure 4, occupies a position relatively similar to that of therod 30.

It Will now be appreciated that, as one portion of the grid wireassembly is subjected to an electrostatic force of a magnitude whichwould otherwise cause the wires thereof to leave their normal position,these wires must overcome the restraining effect of the damp rod withwhich they are in contact. However, this same damp rod contacts anotherportion of the grid wire assembly the wires of which are not subject toa force of this particular value. In fact, the direction in which theforce on the last-mentioned grid wire portion is changing may bedirectly opposed to the direction of changes of the force acting on thefirst group of wires. The damp rods, by contacting all of the wires, actas an equalizing, or balancing medium which almost completely cancelsout any tendency toward movement the individual wires of thecolor-control grid structure may possess.

Although any number of zig-zag damp rods may obviously be employed,three rods each .003" to .005 in diameter have been found suitable inactual tube constructions.

In order to insure that each of the rods 30, 32 and 34 remains in itsproper position as shown in the drawings, a small amount of bindingmaterial, such, for example,

as Sauereisen cement, may be applied near the two extremities of eachrod. As illustrated in Figure 3, this binding inaterial identified bythe reference numeral 36, secures the respective ends of each rod-towhatever number-'of-gr'id wires (such as threeor tour) that-arecontaetedbythe'cement. This positions each rod with respect to the wiresand prevents any-relative movement therebetween 'in the plane of thelatter. Inasmuch as the two extremities of each rod respectively lieoutside the raster area of the target electrode,thereis no noticeableeifect produced by -the cement on the image presented to an observer.'While "this process is entirely satisfactory, other-methods of holdingthe rods in place are possible and are intended to 'fall within thescope of the present disclosure. It will be appreciated, however,thatcertainzconditions of wire spacing and/ or damp rod diametentorexample, make 'it possible to omit the binding material entirely .as therods will remain in position without such aid.

Any material maybe used for the damp rods 30, 32 and 34 which willproduce satisfactory results, especially if this material be of avitreous nature. One substance which has been found to be especiallysuitable is what is known commercially has ..Gl2-glass. When damp rodshaving such a composition are utilized, it is noticed that theelectron'shadow (which each damp rod would normally be expected tocast=upon the phosphor-coated surface 2% of the target electrode, andwhich condition is recognized in copending Cook application Serial No.343,887 filed March 23, 1953) is not visible 'when V1/ V2 is roughlyequal to A, where V2 isthe potential difierence from the cathode toscreen 20 and V1 is the mean potential difference-from the cathode tothe wire grid .22. Reducing this voltage ratio causes an increasingamount of shadow.

It should be understood that use in the present application of theexpression adjacent to in describing the spatial relationship of thewire grid and target electrode is to be interpreted as describing acondition wherein the wire grid lies in a plane slightly spaced apartfrom the plane of the target electrode, and .is not to be confused witha case where these two members are contiguous, or actually in physicalcontact with one another.

Having thusdescribed the invention, what'is claimed is:,

1. .A vibration-inhibiting element for .a cathode-ray tube designed forthe reconstitution of polychrome images and having-a grid structure ofcoplanar parallel wires lying between the cathode-ray beamdevelopingmeans of said tube and the target electrode scanned ttherebyand substantially adjacentto the target, .said vibrationinhibitingelement comprising a nonlinear rod of substantially inflexibleinsulating material extending substantially transverselyto the parallelwires of said vgrid structure and interwoven therebetweenin such amanner as to retain a coplanar wire relationship.

2. A vibration-inhibiting element according to claim 1, in which thenon-linearity of said rod is of a zig zag nature. V y

3. A vibration-inhibiting assembly for a cathode-ray tube designed forthe reconstitution of polychrome images, said tube having aplanar-surfaced target electrode and a grid structure ofcoplanarparallel wires lying adjacent to the -planar surface of said targetelectrode, said vibration-inhibiting assembly including a plurality of;rodlike insulating members each having a permanent .Zigzagconfiguration, each extending substantially transversely to the parallelwires of said grid structure-and interwoven therebetween, the zig-zagconfiguration of each of the said rod-'likemembers being such that theinterwoven relationship of each said zigzag member with the parallelwires of .said grid structureresults in the iormer contacting each ofthe said wires and at the same .timesubtantially retains thesaid'coplanar grid wire relationship.

4. A'vibration-inhibiting assembly according to claim 3, in which anyselected one of the said plurality -of rod-like members contacts .eachparticular wire of said grid structure at a point which is substantiallydiametrically opposed to the point at which such particular wire iscontacted by the one or more rod-like members lying adjacent to the saidoneselected member.

5. A zig-zag damp rod of insulating material for inhibiting vibration ofthe tautly stretched linear conductors forming a color control gridstructure of a cathode-ray tube designed for the production ofpolychrome images, said linear conductors lying adjacent to the targetelectrode of said cathode-ray tube, said damp rod extending transverselyto the conductors of the grid and interwoven therewith and beingessentially of a linear nature and substantially inflexible but beingbent in-and-out at points substantially corresponding in number to thenumber of linear conductors making up said grid structure, the directionof bending of sa-iddamp rod being the same at alternate points, so thatthe said bent rod 'is substantially symmetrical about its longitudinalaxis and adjacent conductors of the grid lie on opposite sidesof therod.

6. In a cathode-ray'tube designed for the production of polychromeim-ages,..the combination of a color-control grid-structure of parallelwires arranged in coplanar rela tion in a plane adjacent to the targetelectrode of said cathode-ray tube, and at least one rod-like element ofsubstantially inflexible insulating material respectively bentin-and-out at equally spaced points corresponding in number essentiallyto the number of parallel wires making up said grid structure, saidrod-like element being adapted for interweaving with the said parallelwires without disturbingthe coplanar relationship of the latter, wherebythe tendency of said-wires to vibrate whencolorcontrol potentials areapplied to said grid structure will be strongly inhibited.

7. A vibration-inhibited color grid assembly for a cathode-ray tubeadapted for thereconstitution of images in color on the tube targetsurface, which comprises a color-control grid structure constituted of amultiplicity of linear conductors all in substantially coplanar'relationship and supported from and located by the tube wall in tautlystretched'relationship adjacent to the target, a non-linear rod ofinsulating material extending transversely to the linearconductors ofthe grid and interwoven therewith, the rod non'linearity being ofa-generally zig-zag configuration with a zig-zag pitch being such as toplace adjacent linear conductors of the grid on opposite sides of therod and alternate linear 'conductors on the same side of the rod andthe-displacement of each zigzag bend from linearity being-such that wheneach linear conductor of the grid rests adjacent to the rod on onesideor the other thereof-and the'group of linear conductors forming :thegrid is maintained by the rod in substantially non-vibratory coplanarrelationship.

References Cited in the file of this patent UNITED STATES PATENTS2,072,638 'Jobst ,Mar. 2, 1937 2,231,691 Snyder Feb. 11, 1941 2,416,056Kallmann Feb. 118, 1947 2,441,791 Schroeder Aug. 10, ,1948 2,461,515Bromwell Feb. 15, '1949 2,568,448 Hanson Sept. 18, 1951 2,653,263Lawrence Sept. '22, 1953 2,757,303 Silverman July' 31, 1956

